Sofc-conduction

ABSTRACT

A solid oxide fuel cell (SOFC) system included high thermal conductivity materials such as copper  10  increase thermal energy transfer by thermal conduction. The copper is protected from oxidation by nickel electroplating and protected from thermal damage by providing Hastelloy liners inside combustion chambers. Monel elements are used in the incoming air conduits to prevent cathode poisoning.

1 COPYRIGHT NOTICE

A portion of the disclosure of this patent document may contain materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever. The following notice shall apply to (his document: ©2014 Protonex Technology Corporation.

2 BACKGROUND OF THE INVENTION 2.1 Field of the Invention

The exemplary, illustrative, technology herein relates to Solid OxideFuel Cell (SOFC) systems, methods of use, and methods of manufacturingSOFC systems. In particular, the exemplary, illustrative technologyrelates to improved systems and methods for thermal energy managementwithin the SOFC system.

2.2 The Related Art

A conventional SOFC system includes a hot zone, which contains or atleast partially encloses system components that are maintained at higheroperating temperatures, e.g. above 350 or 500° C., during operation,depending on the SOFC technology. The hot zone houses an SOW energygenerator or solid oxide fuel cell stack. Conventional SOFC fuel cellstacks are formed by one or more fuel cells with each cell participatingin an electro-chemical reaction that generates an electrical current.The fuel cells are electrically interconnected in series or in parallelas needed to provide a desired output voltage of the cell stack. Eachfuel cell includes three primary layers, an anode layer or fuelelectrode, a cathode layer or air electrode and an electrolyte layerthat separates the anode layer front the cathode layer.

The anode layer is exposed to a gaseous or vaporous fuel that at leastcontains hydrogen gas (H₂) and/or carbon monoxide (CO). At the same timethe cathode layer is exposed to a cathode gas such as air or any othergas or vaporous oxygen (O₂) source. In the cathode layer oxygen (air)supplied to the cathode layer receives electrons to become oxygen ions(O⁺). The oxygen ions pass from the cathode layer to the anode layerthrough the ceramic electrolyte layer. At the triple phase boundary, inthe anode layer, hydrogen (H₂) and/or carbon monoxide (CO) supplied tothe anode layer by the fuel react with oxide ions to produce water andcarbon dioxide and electrons entitled during this reaction produceelectricity and heat Other reaction by products in the fuel stream mayinclude methane, ethane or ethylene. The electricity produced by theelectro-chemical reaction is extracted to DC power terminals to power anelectrical load.

Common anode materials include cermets such as nickel and doped zirconia(Ni-YSZ), nickel and doped ceria (Ni-SDC and or Ni-GDC), copper anddoped ceria. Perovskite anode materials such as (La1-xSrx)Cr1-yMyO3-δ(LSCM) and other ABO₃ structures am also usable. Common cathodematerials include lanthanum Strontium Cobalt Oxide (LSO), lanthanumStrontium Cobalt Iron Oxide LSCF and lanthanum Strontium Manganite(LSM). The electrolyte layer is an ion conducting ceramic, usually anoxygen ion conductor such as yttria doped zirconia or gadolinium dopedceria. Alterably the electrolyte layer is a proton conducting ceramicsuch as barium cerates or barium ziconates. The electrolyte layer actsas a near hermetic barrier to prevent the fuel and air from mixing andcombusting.

Conventional SOFC systems use cross flow or parallel flow heatexchangers, commonly referred to as recuperators, to heat cathode gasses(air) entering the SOFC system. The gas flow heat exchangers heat coolair entering the hot zone exchanging thermal energy between the coolentering air and hot exhaust gas exiting the hot zone.

It is known to include one or more thermal energy or heat sourcesdisposed inside the SOFT hot zone to heat the air and fuel flowingthrough the SOFC system and to heat the fuel cells. The heat source mayinclude a tail gas combustor used to combust spent fuel mixed with hotexhaust, air as the spent fuel and exhaust air exit the cell slack. Asecond heat source may include a cold start combustor operable tocombust fuel at system startup to heat the SOFC surfaces and to heatincoming fuel flowing to the cell stack at least until the SOFC systemsreaches it steady state operating temperature or the CPOX or TGC lightsoff. Electrical heating elements axe also usable instead of or inaddition to a cold start combustor to heat air, fuel, and operatingsurfaces at startup.

In conventional SOFC systems thermal energy is primarily transferred bygas to gas or gas to surrounding surface thermal energy exchange, i.e.primarily by convection. This occurs in the (ail gas combustor whenspent fuel is mixed with hot exhaust air and combusted inside acombustion enclosure. In this case thermal energy is exchanged byconvection as cooler gasses enter the combustion enclosure mix withhotter gases and combust. Additionally convective thermal energytransfer also heats the combustion enclosure surfaces as gas passesthermal energy to the enclosure surfaces. Meanwhile the hot enclosurewalls transfer thermal energy back to cooler gases entering thecombustion chamber when hot surfaces emit thermal energy and gasesflowing proximate to the hot surfaces are heated by the emittedradiation.

In conventional SOFC systems, a recuperator or gas counter flow heatexchanger, is disposed to receive hot gases exiting from the combustionchamber and to receive cool gases entering into the SOFC system inseparate counter flow conduits separated by a common wall. Againconvection and radiation are the dominant thermal energy transfermechanisms as hot gases from the combustor heat conduit walls as theypass to un exit port and the conduit walls heat incoming air. In shortthe thermal energy exchange both inside the tail gas combustor andinside the recuperator is not efficient. The result is that conventionalSOFC systems are notoriously difficult to control and often develop hotspots, e.g. in the combustion enclosures, that can damage the enclosurewalls even burning through walls when a combustion enclosure wall getstoo hot. Alternately when the temperature of the SOFC system is lowered,e.g. by modulating a fuel input flow rale, incomplete fuel processingresults in carbon formation on anode surfaces which ultimately leads todecreased electrical output and eventual failure.

To better address hot and cold spots conventional SOFC systems ofteninclude a plurality of thermocouples or thermistors disposed at varioussystem points to monitor temperature and adjust operation in order toavoid hot spots and prevent cold spots which lead to carbon formation onanode surfaces. However the temperature sensing and monitoring systemsare costly and prone to failure due to the high operating temperaturesof the SOFC systems (e.g. 350-1200° C.). Moreover the need to modulatefuel input as a safety measure to avoid damaging the SOFC system leadsto inefficient and variable electrical power output. Thus there is aneed in the art to avoid thermal gradients and eliminate hot spots inorder to avoid damaging the SOFC system and in order to deliver moreconsistent electrical power output with improve power generationefficiency.

Conventional SOFC systems are generally fabricated from specialtymaterials in order to survive the effects of extended operation at hightemperatures and the severely corrosive environment which continuouslyoxidizes metal surfaces sometimes to the point of failure. Other hightemperature problems that have been addressed in conventional SOFCsystems include the need to match or account for differences in thethermal coefficient of expansion of mating parts of dissimilar materialsin order to avoid loosening between mating parts, cracking of ceramicelements or bending of metal elements, and the need to account forincreased metal creep rates that, occur at high temperature. Inconventional SOFC systems these problems have been addressed by usingspecialty high temperature corrosion resistant nickel-chromium alloyssuch as Inconel or the like. However chromium leached into incomingcathode air can poison the cathode material layer, so materials thatcontain chromium are not desirable along any of the incoming airconduits or heaters if cathode poisoning is to be avoided. Thus whilethere is a need in the art to use corrosion or oxidation resistant hightemperature metals alloys to fabricate SOFC hot zone elements many ofthese alloys contain chromium and them is a further need in the art toavoid contacting cathode air with chromium containing surfaces.

While some thermal energy is transferred between regions of conventionalSOW systems by thermal conduction, e.g. conducted across interconnectedmetal elements, the fact (hut hot and cold spots are still problematicin conventional SOFC systems suggests that thermal conduction is eithertoo slow or insufficient to promote a uniform temperature acrossdifferent regions of a conventional SOFC system. This is due in part tothe need to use specialty metals for the high temperature corrosiveenvironment which have less than desirable thermal conductivityproperties. As an example, Inconel has a thermal conductivity rangingfrom 17-35 W/(m° K) over a temperature range of 150 to 875° C. ascompared to copper which has a thermal conductivity approximatelyranging from 370 W/(m° K) at 500° C. and 332 W/m° K at 1027° C. Thuscopper has a thermal conductivity that is more than 10 times the thermalconductivity of Inconel, which is about 70% nickel. While copperprovides increased thermal conductivity over high temperature metalalloys, mostly comprising nickel, which could improve temperatureuniformity in SOFC systems, copper is readily oxidized in the SOFCenvironment and has thus far been avoided as an SOFC housing material.

3 OBJECTS OF THE INVENTION

In view of the problems associated with conventional methods andapparatus set forth above, it is an object of the present invention toprovide a SOFC system in which increased thermal energy transfer bythermal conduction is used in transfer thermal energy from one area of aSOFC hot zone to another in order to reduce thermal gradients across thehot zone.

It is a further object of the invention to provide interconnectedthermal energy conduction pathways that extend across a plurality ofdifferent mechanical elements that are mechanically interfaced with eachother in order to reduce thermal gradients across the SOFC system.

It is a still further object of the present invention to manage thermalenergy exchange between different regions of a SOFC system hot zone byproviding high thermal conductivity thermal mass elements in thermalcommunication with enclosure walls and with heat sources and heatexchangers to substantially stabilize the temperature of each region ofthe SOFC hot zone.

4 BRIEF SUMMARY OF THE INVENTION

The present invention overcomes the problems associated withconventional SOFC systems by providing an improved SOFC system. Theimproved Solid Oxide Fuel Cell (SOFC) system of the present inventionincludes hot zone enclosure walls disposed to enclose a hot zone cavity.The hot zone enclosure walls are fabricated from one or more materialshaving a thermal conductivity of greater than 100 W/(m° K) attemperatures above 350° C. and preferably with a thermal conductivity ofgreater than 300 W/(m° K). Ideally the hot zone enclosure walls arefabricated from copper. The copper is protected from oxidation byforming a surface coating over exposed surfaces of the enclosure wallsto prevent the enclosure walls from exposure to hydrocarbon fuels and orair. In one example embodiment the surface coating is nickel platingapplied by an electro-plating process to a thickness of at least 0.0005inches but ranging up to 0.0015 inches and even higher to about 0.002inches in some applications in order to prevent oxygen diffusion throughthe plating material at operating temperatures of 350 to 1200° C. Inpractice, the plating thickness is dependent upon the desired operatinglife in hours, the average and/or peak operating temperatures and theoxidants used, e.g. in the fuel or the cathode gas.

At least one thermal mass element is disposed inside the hot zone cavitysupported by or attached to the hot zone enclosure walls. Specificallythe thermal mass element is in thermally conductive communication withthe hot zone enclosure walls. The thermal mass element is fabricatedfrom one or more materials having a thermal conductivity of greater than100 W/(m° K) at temperatures above 350° C. and preferably with a thermalconductivity of greater than 300 W/(m° K). Ideally the thermal masselement Ls fabricated from copper. The copper is protected fromoxidation by forming a surface coating over exposed surfaces of thethermal mass element to prevent the thermal mass element from beingexposed to hydrocarbon fuels and or air or oxygen. Ideally the surfacecoating is nickel plating applied by an electro-plating process to athickness of at least 0.0005 inches and ranging up to 0.002 inches inorder to prevent oxygen diffusion through the plating material atoperating temperatures of 350 to 1200° C. The enclosure walls and thethermal mass may also be fabricated from one or more of molybdenum,aluminum copper, copper nickel alloys or a combination thereof.

A tail gas combustor region is disposed inside the hot zone cavity forcombusting a mixture of spent fuel anti hot exhaust air exiting from theSOFC stack. Alternately the tail gas combustor region may be disposedoutside the hot zone cavity e.g. surrounding the hot zone enclosurewalls. The combustion region is at least partially bounded by the hotzone enclosure walls such that thermal energy received by the hot zoneenclosure walls front combustion is then thermally conducted through thehot zone walls to other regions of the hot zone enclosure walls toreduce thermal gradients across the hot zone enclosure wall structure.The tail gas combustor region is lined by internal walls formed from ahigh temperature, corrosion resistant metal such as Hastelloy and orInconel or ceramic coated steel. More general the liner material is ametal alloy having as its primarily component metal nickel. The liner orliners may be soldered in place in a manner that prevents gasses insidethe tail gas combustor from oxidizing or otherwise damaging surfaces ofthe hot zone cavity and or surfaces of any thermal mass elementsbounding the hot zone cavity.

A recuperator chamber is disposed inside the hot zone cavity forreceiving cool air entering the hot zone cavity and heating the cool airbefore it Is delivered to the SOFC stack. Alternately the recuperatorchamber may be disposed outside the hot zone cavity e.g. surrounding thehot zone enclosure walls or surrounding the combustor region. Therecuperator chamber is at least partially bounded by the hot zoneenclosure walls which radiate thermal energy into the recuperatorchamber to heat incoming air. Alternately or additionally therecuperator chamber is at least partially bounded by walls of thecombustor region. Preferably a thermal mass element forms a portion of atail gas combustor region end wall that is also a recuperator chamberend wall such that a wall including the thermal mass element separatesthe tail gas combustor region from the recuperator chamber. Combustionbyproducts exiting the tail gas combustion region flow over externalsurfaces of the recuperator chamber to further heat the hot zoneenclosure walls surrounding the recuperator chamber.

A fuel reformer may be disposed at least partially inside the hot zoneenclosure for catalyzing or otherwise reforming a fuel supply enteringthe fuel delivery system.

A cold start combustion chamber may be enclosed by the hot zoneenclosure walls for combusting fuel during a cold start of the SOFCsystem. The cold start combustion chamber is at least partially enclosedby the hot zone enclosure walls. Internal walls of the cold startcombustion chamber are preferably lined with a high temperature,corrosion resistant metal such as Hastelloy and or Inconel or a ceramiccoaled metal or fabricated from ceramic insulation.

A SOFC fuel ceil stack is disposed inside the hot zone cavity. The fuelcell stack at least includes one electro-chemical fuel cell andpreferably includes a plurality of fuels cells. Each fuel cell includesan anode support layer, ceramic electrolyte applied over the anodesupport layer and a cathode layer formed over the ceramic electrolytelayer. The anode support layer is exposure to a hydrocarbon fuel whilethe cathode layer is exposed to a cathode gas comprising oxygen. Theanode support layer may be formed as a Hat plate or as a tube shapedconduit.

5 BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention will best be understood from adetailed description of the invention and example embodiments thereofselected for the purposes of illustration and shown in the accompanyingdrawings in which:

FIG. 1 depicts a schematic view of a first exemplary SOFC systemaccording to the present invention.

FIG. 2 depicts a schematic view of an exemplary hot zone of a SOFTsystem according to the present invention.

FIG. 3 depicts a schematic view of exemplary fuel flow pathways of aSOFC system according to the present invention.

FIG. 4 depicts a schematic view of exemplary air flow pathways of a SOFCsystem according to the present invention.

FIG. 5A depicts a section view taken through a first exemplary hot zoneexternal wall of a SOFC system according to the present invention.

FIG. 5B depicts a section view taken through a second exemplary hot zoneexternal wall of a SOFC system according to the present invention.

FIG. 5C depicts a section view taken through an exemplary bottom tubesupport wall including a thermally conductive mass of a SOFC systemaccording to the present invention.

FIG. 5D depicts a section view taken through an exemplary combustionregion end wall including a thermally conductive mass of a SOFC systemaccording to the present invention.

FIG. 5F depicts u section view taken through an exemplary combustionregion bottom wall including a thermally conductive mass of a SOFCsystem according to the present invention.

FIG. 6 depicts a schematic top section view of a SOFC system having aplurality of rod shaped fuel cells arranged in two concentric circularpatterns according to the present invention.

5.1 DEFINITIONS

The following definitions are used throughout, unless specificallyindicated otherwise:

TERM DEFINITION Hastelloy A group of alloys comprising predominantlymetal nickel plus molybdenum, chromium, cobalt, iron, copper, manganesetitanium, zirconium, aluminum and tungsten in varying percentagesincluding zero in some alloys. Hastelloy alloys are primarily used foreffective survival under high temperature and or high stress in moderateto severely corrosive environments. Available from Haynes InternationalInc. of Kokomo IN, USA. Monet A group of alloys comprising up to 67%metal nickel and about 30% copper with smaller amounts of iron,manganese, carbon and silicon. Monel is used for its resistance tocorrosion. Available from Special Metals Corp. of New Hartford NY, USA.SOFC Solid Oxide Fuel Cell Inconel A family of austeniticnickel-chromium alloys comprising nickel 40-70% chromium 14-30%, iron3-9% manganese 0.3-1% plus silicon, carbon, sulfur and other elementsused for its resistance to oxidation and corrosion and strength over awide range of temperatures. When heated, Inconel forms a thick stablepassivating oxide layer protecting the surface from further attack.Attractive for high temperature applications to reduce creep. Availablefrom Special Metals Corp. of New Hartford NY, USA Cermet Any of a classof heat-resistant materials made of ceramic and sintered metal. Oftenformed and sintered as a ceramic oxide mixture and converted through thereduction from an oxide ceramic to the metallic phase. (NiO-YSZ →Ni-YSZ) Perovskite A ternary material with the general structureA^([12])B^([16])X-₃ ^([6]) same type of crystal structure as calciumtitanium oxide (CaTiO₃).

Item Number List

The following item numbers are used throughout, unless specificallyindicated otherwise.

ITEM NUMBER DESCRIPTION 100 SOFC system 105 Hot zone 110 Cold zone 115Enclosure walls 120 Hot zone cavity 125 Air gap 130 Thermal insulation135 SOFC fuel cell stack 140 DC current output terminals 145 Electrolytesupport 150 Anode surface 155 Cathode surface 157Thermocouple/temperature sensor 160 Fuel input line 165 Fuel reformer170 Air input line 175 Recuperator 180 Combustor 185 Exhaust port 190Electronic controller 195 Cold start module 197 Fuel delivery controller198 Air delivery controller 2000 Hot zone 2002 Hot zone enclosure sidewall 2004 Disc-shaped top wall 2005 SOFC fuel cell stack 2006Disc-shaped bottom wall 2010 Hot zone cavity 2012 Thermal insulationlayer 2015 Hot zone enclosure walls 2020 Reformer 2025 Fuel air mixture2030 Reformer enclosure walls 2035 Catalyzing cavity 2040 Catalyzingmedium 2045 Reformer input port 2050 Reformer exit port 2055 Fuel inputmanifold 2060 Longitudinal axis 2065 Annular thermal insulating element2070 Top tube support wall 2075 Bottom tube support wall 2080 Fuel cells2085 Annular tube wall 2090 Cathode chamber 2095 Top end cap 2100 Bottomend cap 2105 Attaching end 2110 Supporting end 2115 Cell input port 2120Cell output port 2125 Electrical Lead 2130 Electrical lead 2135 Tail gascombustor 2140 Combustor end wall 2145 Cathode feed tube 2150 Exit portcombustor 2155 Air gap 2160 Thermally conductive mass 2165 Hot zone exitport 2170 Fuel input manifold top wall 2175 Thermally conductive mass2180 Thermally conductive mass 2185 Combustor baffle 2200 Incoming air2205 Air input port 2210 Recuperator chamber 2215 Recuperator baffle2220 Exhaust out 2225 Air input port 2230 Recuperator air input port2235 Recuperator air output port 2240 Cathode chamber air input port2245 Cathode chamber air output port 2300 Cold start combustor 2305Annular combustor cavity 2310 Combustor inlet port 2315 Fuel 2320Igniter 2325 Startup combustor exit port 5005 Section of wall 2002 5010Copper core 5015 Nickel layer 5020 Nickel layer 5025 Sidewallrecuperator chamber 5030 Hastelloy liner element 5035 (doesn't exist)5040 Section of bottom tube wall 5045 Monel liner element 5050 Hastelloyliner element 5055 Section of wall 2175 5060 Hastelloy liner element5065 Monel liner element 7000 SOFC system 7010 Cathode chamber 7015 Hotzone enclosure wall 7020 Insulation layer 7025 Cathode feed tube 7030Center axes 7035 Inner circular pattern 7040 Inner rod shaped fuel cells7045 Outer circular pattern 7050 Outer rod shaped fuel cells

5.2 DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a schematic diagram of a first embodiment of thepresent invention depicts a Solid Oxide Fuel Cell (SOFC) system (100).The system (100) includes a hot zone (105), that includes at least oneSOFC fuel cell and preferably a plurality of fuel cells forming a fuelcell stack maintained at a high operating temperature, and a cold zone(110) that includes fuel input and exhaust modules, a DO power outputmodule and other control elements. Hot zone enclosure walls (115) aredisposed to enclose a hot zone cavity (120) therein. A thermalinsulation layer (130) surrounds the enclosure walls (115) to thermallyinsulate the hot zone (105). An air gap (125) is provided between theinsulation layer (130) and a side wall of the hot zone enclosure walls(115) and the air gap provides a gas flow conduit for gases to flow fromdifferent regions of the hot zone to an exhaust port (185).

According to an important aspect of the present invention, the hot zoneenclosure walls (115) and associated thermal energy management elementsdescribed below are in thermal communication with each other in order toprovide thermally conductive pathways for thermal energy transfer to allregions of the hot zone by thermal conduction through the hot zoneenclosure walls (115). More specifically the hot zone enclosure walls(115) and any thermal energy management elements, described below,comprise materials having a high coefficient of thermal conductivity,e.g. between 100 and 300 W/(m° K), and preferably above 200 W/(m° K) attemperatures ranging from 350 to 1200° C. Accordingly, the externalwalls and other thermal energy management elements, described below, arefabricated from one or more of copper, molybdenum, aluminum copper,copper nickel alloys or a combination thereof. Specifically the hot zoneenclosure walls (115) and associated thermal energy management elementsare configured to provide thermally conducive pathways for rapidconduction of thermal energy from one area of the hot zone to another.More specifically the hot zone enclosure walls (115) and associatedthermal energy management elements are configured to manage thermalenergy within the hot zone by rapidly conducting thermal energy fromhigh temperature areas of the hot zone to lower temperature areas of thehot zone in order to ensure that the entire hot zone is maintained at asubstantially uniform temperature.

An electrochemical energy generator or fuel cell stack (135) comprisingone or more Solid Oxide Fuel Oils or fuel cells is enclosed within thehot zone (105) and supported with respect to the enclosure walls (115)by one or more support elements, described below. The fuel cell stack(135) includes one or more fuel cells with each cell participating in anelectro-chemical reaction that generates an electrical current. The fuelcells are electrically interconnected in series or in parallel as neededto provide a desired output voltage of the cell stack (135). Each fuelcell includes three primary layers, an anode layer or fuel electrode(150), a cathode layer or air electrode (155) and an electrolyte layer(145) that separates the anode layer from the cathode layer.

The anode layer (150) is exposed to a gaseous or vaporous fuel that atleast contains hydrogen gas (H₂) and/or carbon monoxide (CO). At thesame lime the cathode layer (155) is exposed to air or any other gas orvaporous oxygen (O₂) source. In the cathode layer (155) oxygen (air)supplied to the cathode layer receives electrons to become oxygen ions(O²⁻). The cathode reaction is ½O₂+2e⁻=O²⁻, sometimes written as O

.

The oxygen ions pass from the cathode layer to the anode layer (150)through the ceramic electrolyte layer (145). In the anode layer hydrogen(H₂) and/or carbon monoxide (CO) supplied to the anode layer by the fuelreact with oxide ions to produce water and carbon dioxide and electronsemitted during this reaction produce electricity and heat. Otherreaction by products may include methane, ethane or ethylene. Theelectricity produced by the electro-chemical reaction is extracted to DCpower terminals (140) to power an electrical load.

Common anode materials include cermets such as nickel and dopedzirconia, nickel and doped ceria, copper and ceria Perovskite anodematerials such as Sr₂Mg_(1-x)MnxMoO₆₋₆ orLa_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ) are also usable. Commoncathode materials include lanthanum Strontium Cobalt Oxide (DSC),lanthanum Strontium Cobalt Iron Oxide LSCF and lanthanum StrontiumManganite (LSM). The electrolyte layer is an ion conducting ceramic,usually an oxygen ion conductor such as yttria doped zirconia orgadolinium doped ceria. Alterably the electrolyte layer is a protonconducting ceramic such as barium cerates or barium ziconates. Theelectrolyte layer acts as a near hermetic barrier to prevent the fueland air from mixing and combusting.

Generally each fuel cell is configured with one of the anode layer(ISO), the cathode layer (155) or the electrolyte layer (145) formed asa support or mechanically structural element and the other two layersare coated onto the support element e.g. by dipping, spraying or thelike. Various support element structures are usable including onenon-limiting example embodiment shown in FIG. 2 wherein each fuel cellcomprises an anode support element configured as a hollow tube forming acylindrical gas conduit wherein the anode layer (150) forms the insidediameter of the cylindrical conduit, the ceramic electrolyte layer (145)is coated over the outside diameter of the structural anode layer (150)and the cathode layer (155) is coated over the outside diameter of theelectrolyte layer (145).

A hydrocarbon fuel at least comprising hydrogen (H₂) and carbon monoxide(CO) flows through the hollow ceramic tube in contact with the anodelayer and air flows over and outside surface of the hollow tube incontact with the cathode layer. Electrical current is generated asdescribed above.

While the specific cell stack of FIG. 2 comprises a plurality of tubularfuel cells, other cell slacks formed by fuel ceils having differentknown form factors are usable without deviating from the presentinvention. These may include a cell stack (135) formed from a pluralityof flat sheet type fuel cells formed in a stack with each cellsincluding a sheet shaped support layer with the other layers coated ontothe support layer and a separator disposed between adjacent flat supportlayer with other layers coated onto the support layer.

A fuel input line (160) delivers gaseous or vaporous hydrocarbon fuelfrom a fuel container stored in the cold zone (110) or from an externalsupply delivered into the cold zone (110). A fuel delivery controller(197) in communication with an electronic-controller (190) is disposedalong the fuel input line (160) in the cold zone to regulate fuel inputvolume or mass flow rate as needed to control the fuel input rate. Thefuel input line (160) delivers fuel into a fuel reformer (165) for fuelprocessing which basically extracts pure hydrogen from the fuel. Thereformed fuel is passed over the anode surface (150) forelectro-chemical reaction therewith. The hydrocarbon fuel may comprisevarious fuel components and mixtures hut at least includes hydrogen (H₂)and/or carbon monoxide (CO).

An air ore cathode gas input line (170) delivers gaseous or vaporousoxygen such as room air or another oxygen source into the cold zone(110) e.g. through an intake fan or the like. An air delivery controller(198) in communication with the electronic controller (190) isoptionally disposed along the air input line (170) in the cold zone toregulate air input volume or mass flow rate as needed to control the airinput rate. The air input line (170) delivers room temperature air intoa recuperator (175) which heats the input air by a thermal energyexchange between fuel and air exiting the hot zone and the incomingcooler air. The heated incoming air is passed over the cathode surface(155) for chemical reaction therewith.

Both the spent fuel and oxygen diminished air exit the cell stack (135)and mix in a combustion region or tail gas combustor (180). The mixtureof unreacted fuel and unreacted air plus reaction byproducts deliveredinto the tail gas combustor (180) spontaneously combusts therein locallygenerating thermal energy. The combustor walls, detailed below, comprisematerials having a high coefficient of thermal conductivity, e.g.between 100 and 300 W/(m° K), and preferably above 200 W/(m° K).Additionally the combustor walls are in thermal communication with thehot zone enclosure walls (115) such that, thermal energy generated bycombustion inside the combustor (180) heats the combustor walls to ahigh temperature which quickly initiates thermal energy transfer to allregions of the hot zone by conductive thermal energy transfer throughthe hot zone enclosure walls (115).

Combustion byproduct exiling form the tail gas combustor (180)comprising hot gas is delivered into the recuperator (175). Therecuperator comprises a cross flow heat exchanger with counter flowconduits provided to transfer thermal energy from the combustion hotbyproduct to cooler incoming air to thereby heat the incoming air beforeit enters the SOFC fuel cell slack (135). After passing through therecuperator (175) the combustion byproduct is exhausted through anexhaust port (185).

A thermocouple or other temperature sensor (157) is affixed to a surfaceof the enclosure walls (115) to sense a temperature thereof and thetemperature information is communicated to the electronic controller(190). The controller (190) is in communication with other electronicelements such as one or more electrically operable gas flow valves, gasflow rate detectors and or modulators, associated with the fuel deliverycontroller (197), the air deli very controller (198) and electricalpower output detectors, or the like, and other elements as may berequited to control various operating parameters of the SOFC (100). Theelectronic controller (190) monitors DC current output as well astemperature measured at the thermocouple and further operates to varythe fuel input and air rates as a means of increasing or decreasing DCcurrent output.

Additionally an optional cold start preheater (195) may be provided topreheat input fuel at start up. The preheater (195) may be a fueligniter usable to ignite a portion of the fuel supply for preheating theenclosure walls and ceramic electrolyte structures or the cold startpreheater (195) may comprise an electrical heater usable to preheatinput fuel, or both.

5.3 EXEMPLARY HOT ZONE ARCHITECTURE

Turning now to FIG. 2 a first non-limiting exemplary embodiment of animproved SOFC system hot zone (2000) according to the present inventionincludes a SOFC fuel cell stuck (2005) comprising a plurality ofindividual fuel cells enclosed within a hot zone cavity (2010). The hotzone cavity (2010) is surrounded by enclosure walls (2015) wherein theenclosure walls are formed from one or more of copper, molybdenum,aluminum copper, copper nickel alloys or a combination thereof. Theenclosure walls are surrounded by a thermal insulation layer (2012)which prevents thermal energy from exiling the hot zone. An air gap(2115) is disposed between the hot zone enclosure walls (2015) and thethermal insulation layer (2012). The air gap (2155) provides a fluidflow conduit that leads to a hot zone exit port (2165) anti is used tocarry exhaust gases out of the hot zone.

The enclosure walls (2015) are configured to provide thermally conducingpathways comprising materials having a coefficient of thermalconductivity, of between 100 and 300 W/(m° K) and preferably more 200W/(m° K). Moreover the thermally conducing pathways are disposed to actas thermal energy conduits suitable for conducting thermal energy fromhigh temperature zones of the hot zone to lower temperature zones of thehot zone in order to more rapidly equalize the temperature of each areaof the hot zone.

5.3.1 REFORMER

The hot zone cavity (2010) of the present non-limiting exemplaryembodiment is a can-shaped cylindrical volume bounded by the hot zoneenclosure walls (2015) which include a cylindrical side wall (2002) adisk-shaped top wall (2004) and a disk shaped bottom wall (2006). Thehot zone (2000) operates most efficiently at a temperature above 350 orabove 500° C. depending upon the SOFC reactions being used and may beoperated at temperatures in the range of 350 to 1200° C. Accordinglyeach of the elements of the hot zone of the present invention isconfigured to operate reliably at temperatures ranging up to 1200° C.

According to a preferred non limiting example embodiment of the presentinvention a fuel reformer (2020) that uses an exothermic reaction toreform fuel is provided inside or partially inside the hot zone toreform the input fuel for delivery into each of the fuel cells of thefuel cell stack (2005). The reformer (2020) of the present exemplaryembodiment comprises a Catalytic Partial Oxidation (CPOX) reactor whichpartially combusts a fuel air mixture (2025) delivered thereto. The fuelreforming process creates a hydrogen rich fuel or syngas comprisinghydrogen, carbon monoxide water, carbon dioxide and other smallhydrocarbons such as methane. The CPOX reactor includes a catalyst suchas a metallic or oxide phase of rhodium (Rh) or other suitablecatalyzers (e.g. Pt, Pd, Cu, Ni, Ru and Ce) coated on internal surfaces(2040) thereof. The fuel air mixture (2025) passing through the CPOXreactor is catalyzed as it passes over the catalyst coated surfaces(2040) and the heat released by the reaction is radiated and thermallyconducted to the hot zone enclosure walls (2015) and helps to heat thefuel cell stack.

The CPOX reformer (2020) comprises reformer enclosure walls (2030)surrounding a cylindrical catalyzing cavity (2035). The cylindricalcatalyzing cavity (2035) supports a catalyzing medium (2040) therein. Inthe present example embodiment, the catalyzing medium is a square cellextruded monolith (2040) with exposed surfaces thereof coated with asuitable catalyst. The monolith is positioned such that the incomingfuel air mixture (2025) flows past the exposed surfaces of the squarecell extruded monolith for catalyzation. Other suitable catalyzingstructures may include a plurality of parallel plate or concentric ringstructures or a porous metal or ceramic foam structure such as asintered or extruded element formed with exposed surfaces thereof coatedwith tire catalyzing agent. Alternately, the catalyzing structure maycomprise a plurality of mesh screens having exposed surfaces coated withthe catalyzing agent. The main fuel air mixture (2025) herein after“fuel” enters the reformer (2020) through a reformer input port (2045)and flows through the catalyzing medium (2040) for catalyzation bycontact with the catalyzed surfaces. The catalyzed fuel flows out of thereformer through a reformer exit port (2050) and into a fuel inputmanifold (2055).

In the present non limiting exemplary embodiment the reformer enclosurewalls (2030) comprises a cylindrical or square wall enclosing acylindrical or square cross-sectioned catalyzing cavity (2035). Thecatalyzing medium, (2040), is supported inside the catalyzing cavity(2035) disposed to force the incoming fuel (2025) to flow through thecatalyzing structure past the catalyzing surfaces. A thermal insulatingelement (2065) is disposed to surround outside surfaces of thecatalyzing cavity (2035). The thermal insulating element (2065) isprovided to substantially prevent thermal energy from entering orexiting the catalyzing cavity (2035). The reformer enclosure walls(2030) may comprise a high temperature steel alloy such as Inconel,comprising nickel chromium and iron, a high temperature copper alloye.g. Monel, comprising nickel and copper, or other suitable hightemperature material.

5.3.2 SOFC FUEL CELL STACK

The SOFC fuel cell stack (2005) is supported inside the can-shaped hotzone enclosure walls (2015). A plurality of rod shaped fuel cells (2080)is supported longitudinally inside a cathode chamber (2090). The cathodechamber (2090) is a can-shaped chamber bounded by the hot zone enclosurecylindrical side wall (2002) and by a pair of opposing disk-shaped topand bottom tube support walls (2070) and (2075). Each tube support wall(2070, 2075) is attached to the cylindrical sidewall (2002) by suitableattaching means such as by welding or brazing, by bracketing andmechanical fastening or held in place without fasteners by a claimingforce, by an adhesive bond, or the like. Preferably the cell stack(2005) is assembled prior to installation into the hot zone enclosurewalls (2015) and is removable from the hot zone enclosure walls (2015)as a unit, e.g. to repair or inspect the cell stack as needed.Accordingly the top and bottom tube support walls (2070, 2075) may becaptured in place between opposing end stops, not shown.

The top tube support wall (2070) mechanically engages with and fixedlysupports a top or input end of each of the plurality of rod shaped fuelcells (2080). The mechanical interface between the top support wall(2070) and each of the plurality of fuel cell input ends is a gas tightinterface in order to prevent the fuel air mixture (2025) in the fuelinput manifold (2055) front entering the cathode chamber (2090). The toptube support wall (2070) is preferably formed with Inconel. Additionallyeach of the top end caps (2095) is also formed with Inconel, which is aneffective material for avoiding creep in high temperature environments.The bottom tube support wall (2075) mechanically engages with andmovably supports a bottom or output end of each of the plurality of rodshaped fuel cells (2080). In particular the output end of each fuel cell(2080) is longitudinally movable with respect to the bottom support wall(2075) in order to accommodate changes in the length of each fuel cellas the fuel cells are healed to an operating temperature between 350 and1200°πC. An example tube support system usable with the presentinvention is disclosed by Palumbo in related U.S. patent applicationSer. No. 13/927,418, filed on Jun. 26, 2013 entitled, SOLID OXIDE FUELCELL WITH FLEXIBLE ROD SUPPORT STRUCTURE.

Referring now to FIGS. 2 and 5D, the bottom tube support wall (2075)includes a disk shaped thermally conductive mass (2180) comprising oneor more materials having a coefficient of thermal conductivity, of morethan 100 W/(m° K) and preferably more than 200 W/(m° K) such as one ormore of copper, molybdenum, aluminum copper, copper nickel alloys or acombination thereof. The disk shaped thermally conductive mass (2180) isprotected by top and bottom protective surface layers (5045) and (5050)described below in relation to FIG. 51>. In one non-limiting exemplaryembodiment, each top (5045) and bottom (5050) protective surface layercomprises a separate disk shaped element in thermally conductive contactwith the disk shaped thermally conductive mass (2180). Specifically, thetop surface layer (5045) facing the cathode chamber (2090) comprises adisk-shaped chromium free high temperature metal alloy such as Monel andthe bottom surface layer (5050) that faces a combustion region (2135),or tail gas combustor, comprises a disk-shaped high temperature,corrosion resistant metal such a Hastelloy alloy.

Preferably, each of the top and bottom protective surface layers (5045)and (5050) is in thermally conductive contact with the thermallyconductive mass (2180) which is also in thermally conductive contactwith the hot zone enclosure cylindrical sidewall (2020). Accordingly asthe fuel air mixture is combusted in the tail gas combustor or combustorregion (2135) thermal energy generated by combustion is radiated to thewalls enclosing the combustion region (2135) and from the enclosingwalls is thermally conducted to the thermally conductive mass (2180) andto other regions of the hot zone through the hot zone enclosure walls(2015). In addition thermal energy emitted from the thermally conductivemass (2180) is radiated into the cathode chamber (2090) where it heatsthe cathode gas, or air flowing there through and heats surfaces of thefuel cells enclosed therein.

Each of the rod shaped fuel cells (2080) comprises a lube shaped annularwall (2085) wherein the anode layer is the support layer. The tubeshaped annular wall (2085) is open at both ends. The annular wall (2085)forms a fuel conduit (2085) that extends through the cathode chamber(2090) to carry fuel (2025) there through. Other rod shapes includingsquare, triangular, pentagonal, hexagonal or the like, are usablewithout deviating front the present invention. Additionally othersupport layers are usable to provide structural integrity. Each fuelcell includes two metal end caps (2095) and (2100) or tube manifoldadaptors with one end cap attached to each of two opposing ends of thetube annular wall (2085).

Each end cap (2095) and (2100) or tube manifold adaptor comprises a cupshaped attaching end (2105) and a journal shaped supporting end (2110).The attaching end (2105) includes a blind hole sized to receive theoutside diameter of the annular wall (2085) therein. Each attaching end(2105) is fixedly attached to a rod end by a press or inference lit orby another fastening means such as brazing or an adhesive bond usingmaterials suitable for the operating temperature of the hot zone,(350-1200° C.). The journal shaped supporting end (2110) includes anannular wall formed with an outside diameter sized to engage with acorresponding through hole passing through the lop supporting plate(2070) on the input side and a corresponding through hole passingthrough the bottom supporting plate (2075) on the output side. Thejournal shaped supporting end (2110) further includes a through holepassing there through which serves as a cell input port (2115) at thetop end of the rod shaped fuel cell or as a cell output port (2120) atthe bottom end of the rod shaped fuel cell (2080). Preferably theendcaps (2095 & 2100) or lube manifold adaptors each comprise a hightemperature low Cr, corrosion resistant metal alloy thermally compatiblewith the fuel cell. The caps may be comprised of a ceramic coating onthe metal cap to prevent Cr contamination.

Referring to FIGS. 2 and 3, the top end cap (2095) of each fuel cell(2080) may provide electrical communication with an outside diameter orcathode layer of the annular wall (2085) such that the outside diameterof the annular wall (2085) is in electrical communication with one ofthe DO terminals (140) over an electrical lead (2125) through the endcap (2095). A second electrical lead (2130) is in electricalcommunication with an inside diameter of the annular wall (2085) oranode layer and with a different terminal of the DC terminals (140).Additionally electrical insulators (not shown) are provided between eachend cap (2095) and (2100) and the corresponding top and bottom supportwalls (2070) and (2075) to electrically isolate the hot zone enclosurewalls (2015) from electrical current being generated by the cell suck(2005).

Each rod shaped fuel cell is formed by the annular wall (2085) comprisesan anode support layer which is a structural anode material layer formedwith an inside and an outside diameter. The anode support layer maycomprise a cermat comprising nickel and doped zirconia (ZrO₂), nickeland doped ceria (CeO₂), copper and ceria or doped ceria or the like. Theoutside diameter of the anode support layer annular wall (2085) is aleast partially coated with a ceramic electrolyte layer such as a Yttriastabilized zirconia or a cerium (Ce) or lanthanum gallate based ceramic.The outside diameter of the ceramic electrolyte layer is at leastpartially coated with a cathode material layer such as lanthanumstrontium cobalt oxide. (LSO), lanthanum strontium cobalt oxide (LSCF),lanthanum strontium manganite (LSM) or the like.

In a second non-limiting example embodiment of the system (2000) themechanical structure of the hot zone enclosure walls and internal endwalls is similar to that shown in FIG. 2 and described above however;the anode and cathode layers are on opposite sides of the ceramicelectrolyte layer. Specifically in the second embodiment the insidediameter of the anode support, layer annular wall (2085), (as opposed tothe outside diameter), is a least partially coated with a ceramicelectrolyte layer such as a Yttria stabilized zirconia or a cerium (Ce)or lanthanum gallate based ceramic and the inside diameter of theceramic electrolyte layer is at least partially coated with a cathodematerial layer such us lanthanum strontium cobalt oxide (LSC), lanthanumstrontium cobalt oxide (LSCF), lanthanum strontium manganite (LSM) orthe like. In this example embodiment the anode support layer of theannular wall (2085) is an outside diameter of each fuel cell and theinside diameter of each fuel cell is the cathode layer. Thus in thesecond example embodiment the cathode chamber (2090) becomes an anodechamber and fuel is delivered into the anode chamber while the cathodegas, air is flowed through the rod shaped fuel cells.

The fuel mixture (2025) is flowed over the anode material layer whiletire cathode gas, oxygen (air) is flowed over the cathode material layerin order to generate electrical current flow. The current flow passesout of the cell stack over the electrical terminals (2125) and (2130) tothe DC terminals (140) and may be used to power external devices. It isnoted that in other embodiments such as the second embodiment brieflydescribed above, the anode and cathode surfaces can be reversed with thecathode layer on the inside diameter of the fuel cells and the anodelayer on the outside diameter of the fuel cells and air flowing throughthe gas flow conduit formed by the fuel cells and fuel flowing overoutside surface of the fuel cells without deviation from the presentinvention.

The fuel input manifold (2055) comprises a cylindrical chamber boundedby a disk-shaped top wall (2170) and the opposing disk shaped top tubesupport wall (2070). The disk-shaped top wall (2170) includes athermally conductive mass (2160). The thermal mass (2160) comprises oneor more materials having a coefficient of thermal conductivity of morethan 100 W/(m° K) and preferably more than 200 W/(m° K) such as one ormore of copper, molybdenum, aluminum copper, copper nickel alloys or acombination thereof. The thermal mass (2160) is in thermally conductivecommunication with the hot zone enclosure walls (2015) and specificallywith the sidewall (2002). The thermally conductive mass (2160) Ispositioned proximate to an annular cold start, combustion chamber(2305), described below, in order to receive thermal energy from fuelthat is combusted within the cold start chamber (2305) during startupand to thermally conduct thermal energy received therefrom to the hotzone external walls (2015). Additionally, the thermally conductive mass(2160) radiates thermal energy received from fuel combustion within thecold start chamber (2305) and received by thermal conduction through thehot zone enclosure walls to fuel (2025) as it passes through the fuelinput manifold (2055).

The lop lube support wall (2070) forms a gas light seal with thesupporting ends (2110) of each of the fuel cell top end caps (2095).Additionally each of the fuel cells (2080) is fixedly hung from the topsupport wall (2070) by the mechanical interface funned in the topsupporting wall (2070) which includes through holes for receiving thesupporting ends (2110) or manifold adaptors there through. Additionallythe fuel input manifold (2055) is bounded by the cylindrical sidewall(2002).

Since the present exemplary embodiment utilizes a CPOX reformer (2020)which uses an exothermal reaction to reform fuel, the reformer (2020) isa thermal energy source which is beneficially disposed inside the hotzone (2000) to heat incoming fuel (2025) as the fuel enters the hotzone. However in other embodiments of SOFC systems of the presentinvention the reformer (2020) may utilize an endothermic reaction, e.g.a steam reformer or a thermally neutral reaction e.g. an auto thermicreformer to reform the fuel anti in these cases the reformer (2020)would be more beneficially disposed outside the hot zone (2000) andplaced instead in the cold zone (110), shown in FIG. 1. Thus theimproved hot zone (2000) of the present invention can be operatedwithout a reformer (2020) without deviating from the present invention.

5.4 TAIL GAS COMBUSTOR

The tail gas combustor or combustor region (2135) is an annular volumedisposed between the disk shaped bottom tube support wall (2075), whichincludes a thermal mass (2180), both described above and shown in FIG.5D, and a disk-shaped combustor end wall (2140) which also includes athermal mass (2175). Both thermal masses (2180) and (2175) comprise oneor more materials having a coefficient of thermal conductivity of morethan 100 W/(m° K) and preferably more than 200 W/(m° K) such as one ormore of copper, molybdenum, aluminum copper, copper nickel alloys or acombination thereof. The thermal masses (2180) and (2140) are positionedto receive thermal energy from the combustion region (2135) and areconfigured to conduct the thermal energy received from the combustionregion to the hot zone enclosure walls (2015) as well as to radiate thethermal energy received from the combustion region into the cathodechamber (2090) and the recuperator chamber (2210).

An annular combustor baffle (2185) is provided inside the annualcombustor region to redirect gas flow through the combustor region(2135) and create turbulence which increases convective energy transferto the side walls of the combustor region (2135). The combustor baffle(2185) may be fixedly attached to the hot zone enclosure side wall(2002) or may comprise a portion of a combustion chamber liner describedbelow.

A cathode feed tube (2145), described below, passes through thecombustor region (2135) along the central longitudinal axis (2060). Thewalls of the cathode feed tube (2145) are heated by convective thermalenergy transfer from combustion gases inside the combustor region(2135). Air flowing through the cathode feed tube (2145) toward thecathode chamber (2090) is heated by thermal energy radiated from thecathode feed tube (2145) to the air flowing there through.

Internal walls of the combustor region (2135) are lined with a hightemperature, corrosion resistant metal such a Hastelloy alloy. In thecase of the wall disk shaped bottom lube support wall (2140), thesurface facing the combustor region comprises Hastelloy. In the case ofthe combustor region end wall (2175), the surface facing the combustorregion comprises Hastelloy. In each case the wall (2075) and (2175) isformed as a composite structure having a Hastelloy disk shaped liner inthermally conductive contact, with the corresponding thermal mass (2180)and (2140) respectively. The cylindrical side wall of the combustorregion (2135) is also lined with a high temperature, corrosion resistantmetal such a Hastelloy variation which is a nickel based alloy at leastcontaining cobalt, chromium and molybdenum. In one non-limiting exampleembodiment the sidewall liner comprises separate element formed as atube shaped open ended cylindrical wall with the combustor baffle (2185)formed integral therewith. Moreover the side wall liner is formed to beinserted into the hot zone enclosure sidewall (2002) and from either ofits open ends and to make thermally conductive contact with the sidewall(2002) substantially over the entire surface of the wall liner.

5.5 RECUPERATOR

Air (2200) enters the cathode feed tube (2145) through an input port(2205) and flows into a recuperator chamber (2210). The recuperatorchamber (2210) is positioned in close proximity to the tail gascombustor region (2135) in order to heat incoming air (2200) usingthermal energy generated by combustion of the spent fuel occurringinside the combustor region (2135). The recuperator chamber (2210) is anannular chamber surrounding the cathode feed tube (2145) and is boundedon a top side by the disk-shaped combustor end wall (2140), on a bottomside by the disk shaped hot zone enclosure bottom wall (2006) and on itssides by the hot zone enclosure cylindrical side wall (2002).

Thermal energy is conducted to walls of the recuperator chamber (2210)by the hot zone enclosure walls (2105), by the combustor end wall (2140)und to a lesser extent by the cathode feed tube (2145). Thermal energyis radiated from the recuperator chamber walls to the air (2200) as itpasses through the recuperator chamber (2210). Outside walls of therecuperator chamber (2210) are further heated by hot exhaust gassesexiting from the combustor region (2135). In particular the recuperatorchamber (2210) is surrounded by the air gap (2155) which carries hoiexhaust gases exiting from the combustor region (2135) through exitports (2150) to the hot zone exit port (2165). Thermal energy from hotexhaust gases heats outside wall portions of the recuperator chamberwalls by convective heat transfer

A recuperator baffle (2215) is disposed inside the recuperator chamber(2210) and passes through the cathode feed tube (2145) preventing airflow through the cathode feed tube (2145). Thus air (2200) entering thecathode feed tube (2145) through the port (2205) impinges on therecuperator baffle (2215) inside the cathode feed tube and is forcedinto the recuperator chamber (2210) through one or more air input ports(2225). The input air (2200) flowing into the recuperator chamberthrough the air input ports (2225) passes around the recuperator baffle(2215) and reenters the cathode feed tube through one or more air outputports (2235) alter being healed in the recuperator chamber (2210).

5.6 COLD START COMBUSTOR

Referring to FIG. 2, the SOFC hot zone (2000) optionally includes a coldstart fuel combustor provided to initially heat the hot zone to anoperating temperature above 350° C. or at least until spontaneouscombustion occurs in the tail gas combustor region. The cold start fuelcombustor includes an annular startup combustion chamber (2305). Thestartup combustion chamber (2305) surrounds the catalyzing cavity (2035)and the annular thermal insulation (2065). The startup combustionchamber (2305) is bounded on lop by the disk shaped hot zone enclosuretop wall (2004) and on bottom by the disk-shaped fuel input manifold topwall (2170), which includes the annular thermal mass (2175). The startupcombustion chamber (2305) Is further bounded by the hot zone enclosuresidewall (2002).

A startup combustor inlet port (2310) receives uncatalyzed fuel thereinfrom a fuel source, not shown. The uncatalyzed fuel may comprise variouscombustible gaseous or vaporized liquid fuels such as natural gas,propane, methane, hydrogen alcohol, or a mixture of fuels and air. Theuncatalyzed fuel is delivered into the startup combustion chamber (2305)through the combustor inlet port (2310) and is ignited by an electricspark igniter (2320).

During startup combustion, thermal energy generated by fuel combustioninside the startup combustion chamber (2305) is transferred byconvective thermal energy transfer to the hot zone enclosure top wall(2004) and sidewall (2002) as well as to the fuel input manifold topwall (2170). From each of these walls the thermal energy from startupcombustion is thermally conducted to other legions of the hot zone bythe thermal conductive hot zone enclosure walls (2015).

Exhaust gases from the start up combustion exit the startup combustionchamber (2305) through the combustor outlet port (2325) which is influid communication with the air gap (2155) which leads to the hot zoneexit port (2165). Thus the exhaust gases flowing from the startupcombustion chamber (2305) to the hot zone exit port (2165) further heatexternal surfaces of the hot zone enclosure walls (2015) by convectiveheal transfer.

Internal walls of the startup combustion chamber (2305) are lined with ahigh temperature, corrosion resistant metal such u Hastelloy variationwhich is a nickel based alloy at least containing cobalt, chromium undmolybdenum. In the case of the disk shaped hoi zone enclosure top wall(2004) this wall is lined with a Hastelloy material layer on its innersurface wherein the Hastelloy layer is in thermally conductive contactwith the hot zone enclosure top wall (2004). In the case of thedisk-shaped fuel input manifold lop wall (2170), a top side of this wallcomprises a Hastelloy material layer in thermally conductive contactwith the annular thermally conductive mass (2175). In the case of theside walls a cylindrical wall liner comprising a Hastelloy material isinserted into the startup combustion chamber in thermally conductivecontact with the hot zone enclosure wall (2002).

5.7 GAS FLOW DIAGRAMS 5.7.1 Fuel Flow Diagram

Referring now to FIG. 3 a schematic fuel flow diagram depicts the flowpath of the air fuel mixture (2025) as it passes through the hot zone(2000). The fuel (2025) enters the reformer input port (2045) and passesthrough the reformer catalyzing zone (2035) for catalyzation. Thecatalyzed fuel exits the reformer through the reformer exit port (2050)and enters the input manifold (2055). From the input manifold (2055),find enters each of the fuel cells or annular walls (2085) throughcorresponding cell input ports (2115) and flows through each fuel celland exits the fuel cells through corresponding cell output ports (2120).Inside the fuel cell (2080) the fuel reacts with the anode materiallayer forming the inside surface of the cell annular walls (2085). Afterexiting the fuel cells through the cell exit ports (2120) the remainingfuel air mixture (2025), which comprises unreacted fuel and reactionby-products enters the combustor region (2135) where it mixes with airexiting from the cathode chamber (2090) forming a mixture which isspontaneously combusted therein. As described above, thermal energygenerated by combustion in the combustor region (2135) is convectivelytransferred to side walls of the combustor region and thermallyconducted to other regions of the hot zone through the hot zoneenclosure walls (2015). Additionally thermal energy generated bycombustion in the combustor region (2135) may be transfer to each of thethermally conductive masses (2175) and (2180) proximate to the combustorregion by gas to surface thermal transfer by convection and thermalconduction through the enclosure walls. Additionally the thermallyconductive masses (2175) and (2180) proximate to the combustor regionrespectively radiate thermal energy into the recuperator chamber (2210)and the cathode chamber (2090) to heat air passing there through.

After combustion exhaust gases from the combusted mixture (shown as greyarrows) exit the combustor (2135) through one or more combustor exitports (2150) to the air gap (2155). From the air gap (2155) the exhaustgas from the combusted mixture exit the hot zone through a hot zone exitport (2165).

5.7.2 Fuel Flow Diagram Cold Start

As further shown in FIG. 3, unreformed fuel (2315) enters the startupcombustion chamber (2305) through the startup combustor inlet port(2310) where the fuel is combusted.

After combustion exhaust gases (shown as grey arrows) exit the combustor(2135) through one or more startup combustor exit ports (2325) to theair gap (2155). From the air gap (2155) the exhaust gas from the startupcombustor exit the hot zone through a hot zone exit, port (2165).

5.7.3 Air Flow Diagram

Referring now to FIG. 4 a schematic air flow diagram depicts the flowpath of air (2200) as it passes through the hot zone (2000). The air(2200) enters the cathode feed tube (2145) through an air input port(2205). The air (2200) exits the cathode feed tube through a recuperatorair input port (2230) to enter the recuperator chamber (2210). Air flowsaround the recuperator baffle (2215) and reenters the cathode feed lube(2145) through a recuperator air output port (2235). Inside therecuperator chamber (2210) the air (2200) is heated by thermal energyradiated from the recuperator chamber walls (2006), (2002) and thecombustor end wall (2140) and associated the annular thermallyconductive mass (2175).

The air (2200) passes through the combustor region (2135) as it flowsthrough cathode feed tube (2145). In the combustion region the air isfurther heated by thermal energy radiating from surfaces of the cathodefeed tube (2145) before entering the cathode chamber (2090) while stillflowing through the cathode feed tube (2145). The air (2200) exits thecathode feed tube and enters the cathode chamber (2090) through aplurality of cathode chamber air input ports (2240) disposed along aportion of the length of the cathode feed tube (2145) that extends intothe cathode chamber (2090).

Once inside the cathode chamber (2090) the air (2200) fills the cathodechamber and impinges on the outside diameter or cathode layer of each ofthe fuel cells (2080) and reacts with the cathode material layer coatedover at least a portion of the outside diameter of each of the fuelcells. The reaction between air passing over the cathode material layercoupled with the reaction of fuel passing over the anode material layerforming the inside diameter of each of the fuel cells generates acurrent flow which is conveyed to the DC terminals (140) over theelectrical leads (2125) and (2130) shown in FIG. 3.

After reacting with the cathode material layers coated on each of thefuel cells, the oxygen depleted air (2200). (shown as dashed flow lines)exits the cathode chamber (2090) through one or more cathode chamberoutput ports (2245) which lead into the combustor region (2135). In thecombustor region (2135) the oxygen depleted air mixes with hydrogendepleted fuel exiting from the fuel cells und the mixture of iscombusted. Exhaust gasses from the combusted mixture exit the combustorregion (2135) through the combustor exit ports (2150) which lead to theair gap (2155). The air gap (2155) carries the exhaust gasses to the hotzone exit port (2165) and out of the hot zone.

While FIG. 4 schematically shows two diametrically opposing recuperatorair input ports (2230), two diametrically opposing recuperator airoutput ports (2235) and pairs of two diametrically opposing cathodechamber air input ports (2240), however the actual device may includeany bole pattern having one or more holes arranged around thecircumference of the cathode feed tube (2145) as required for air flowdistribution. Similarly FIG. 4 shows two diametrically opposed cathodechamber air output ports (2245) and two diametrically opposing combustorexit ports (2150), however, the actual device may include any holepattern having one or mote holes arranged around the circumference ofthe disk shaped wall (2070) or the cylindrical side wall (2002) as maybe requited for air (low distribution. Alternate any of the gas portsdescribed above may have non-circular shapes e.g. square, rectangular,and oval or slotted without deviating from the present invention.

5.8 ENCLOSURE WALL SURFACE TREATMENTS

According to an aspect of the present invention no copper surface isexposed to oxygen/air in order to avoid oxidation damage to the copper.This includes all surfaces forming the entire fuel flow pathway and allsurfaces forming the entire airflow pathway since both the fuel and theair contain or could contain oxygen. Copper surfaces that may be exposedto fuel flow or to air flow are at least protected by a layer of nickelplating applied to a thickness of 0.0005 to 0.0015 inches, (12.5 to 38.1μm) by electro-deposition plating or the like. The thickness of thenickel plating is more than 100 times the normal thickness ofconventional nickel electro-deposition coatings and the thicker nickelcoating is used to substantially prevent, oxygen diffusion through thenickel coating.

This aspect of the present invention is shown in FIG. 5A which depicts anon-limiting exemplary section view taken through any one of the hotzone cavity walls (2015). The hot zone cavity wall section (5005)includes a copper core (5010) comprising copper having a thermalconductivity approximately ranging from 370 W/(m° K) at 500° C. and 332W/(m° K) at 1027° C. The copper core (5010) has a thickness in the rangeof 0.01-0.125 inches (0.25-3.2 mm) however other thicknesses are usablewithout deviating from the present invention. More generally the hotzone cavity wall thickness may increase or decrease as needed for aparticular application. Generally thicker enclosure walls e.g. up toabout 0.25 inches take longer to heat to a desired operating temperaturebut have the advantage that once heated to the operating temperature thethicker walls have a higher capacity for thermal conduction and are lessprone to thermal gradient formation and provide a longer operating lifethan thinner walls when surface oxidation is the failure mode simplybecause it takes long to for thicker walls oxidize to a degree that thewall becomes unusable.

The copper core (5010) includes two opposing surfaces forming inside andoutside surfaces of the enclosure wall and in a preferred embodimenteach of the inside and outside surfaces of the copper core (5010; iscompletely covered by electro-deposition nickel coating layers (5015) onthe inside surface and (5020) on the outside surface. Each nickelcoating layer is applied to a layer thickness of at least 0.0005 inches.(12.5 μm) which is suitably thick to prevent oxygen diffusion throughthe nickel coating layer. More generally a desired nickel coating layerthickness in the range of 0.0005 to 0.001.5 (12.5 to 38.1 μm) providesadequate surface protection from oxidation for a product life of up toabout 40,000 hours and thicker nickel coatings are usable to increaseproduct life lime without deviating from the present invention.Referring to FIG. 2 the wall section (5005) is at least representativeof outer walls of the hot zone enclosure walls (2015) including thecylindrical side wall (2002), the disk-shaped top wall (2004), the diskshaped bottom wall (2006) and may be representative of some walls of thereformer enclosure walls (2030).

According to an aspect of the present invention combustion chambersurfaces are lined with a high temperature, corrosion resistant metalsuch a Hastelloy alloy in order to protect internal surfaces of thecombustion chamber from surface damage from exposure to hightemperatures, combustion byproducts and corrosive elements. AlternateMonel or Inconel is usable without deviating from the present invention.

This aspect of the present invention is shown in FIG. 5B which depicts anon-limiting exemplary section view (5025) taken through a combustionchamber cylindrical side wall. The side wall section (5025) includestire copper core (5010) of the hot zone enclosure sidewall (2002) andthe electro-deposition nickel coating layers (5015) and (5020) appliedover opposing sides of the copper core as described above. Specificallythe section view (5025) includes the same hot zone external wall (5005)shown in FIG. 5A. In addition the combustion chamber side wall section(5025) further includes a Hastelloy alloy liner (5030) positioned toline the inside surface of the combustion chamber. Referring to FIG. 2the cylindrical side wall section (5025) is at least representative ofcylindrical outer wall of the annular tail gas combustion region (2135)and the cylindrical outer wall of the annular cold start combustionregion (2035). The sidewall section (5025) shows the hot zonecylindrical wall (2002) protected by the Hastelloy alloy liner element(5030). In the specific example of the tail gas combustor chamber (2135)the Hastelloy alloy liner element (5030) also includes the combustorbaffle (2185) attached thereto or formed integral therewith. Howeverexcept for the presence of the combustor baffle (2185) the section(5025) is also representative of the lop and side walls of the annularcold start combustor cavity (2305).

Each of the annular combustor chambers (2135) and (2305) is also linedby a pair of opposing disk shaped Hastelloy alloy liner elementspositioned to line the inside top and the inside bottom surfaces of thecombustor region. In the case of the tail gas combustor region (2135)its chamber top wall is formed by the bottom lube support wall (2075)which includes a disk shaped Hastelloy alloy liner element (5050), shownin FIG. 5C. The liner element (5050) is disposed to face the inside ofthe annular tail gas combustor region or chamber (2135). The tail gascombustor region bottom wall is formed the combustor end wall (2175)which also includes a disk shaped Hastelloy alloy liner (5060) facingthe inside of the annular combustor region chamber (2135).

In the case of the annular combustion cavity (2305) of the cold startcombustor its top chamber wall is formed by the hot zone enclosure topwall (2004) which includes an annular shaped Hastelloy alloy linerelement (5030) in contact with the inside top wall of the annularcombustor chamber (2305). Specifically the hot zone enclosure top wall(2004), also the top wall of the cold start annular combustion cavity(2305) is detailed in the section view of FIG. 5B which shows the coppercore (5010) covered by electro-deposited nickel layers (5015) on theinside surface and (5020) on the outside surface and includes aHastelloy alloy liner element (5030) in contact with the nickel layer(5015). While the section view (5025) is vertically oriented andincludes the Hastelloy baffle (2185) the section is the same as the topwall (2004) without the baffle (2185) and rotated to a horizontalorientation like the top wall (2004).

The bottom wall of the annular combustion cavity (2305) is formed by thetop wall of the fuel input manifold (2170). Ibis wall also includes anannular shaped Hastelloy alloy liner element (5060), similar to the oneshown in FIG. 5D, in mating contact with the inside bottom wall of theannular combustor chamber (2305).

According to an aspect of the present invention no incoming air (2200)is exposed to a surface that is formed from a material that includeschromium in order to avoid poisoning the cathode layer applied toexterior surfaces of the fuel cells (2080). Ibis includes all surfacesforming the entire incoming air flow pathway which includes interiorsurfaces of the cathode feed tube (2145), the recuperator chamber(2210), the recuperator baffle (2215), exterior surfaces of the cathodefeed tube (2145), interior surfaces of the cathode chamber (2090) andelements housed within the cathode chamber including the fuel cell endcaps (2095) and (2100) and the top and bottom fuel cell support walks(2070) and (2075).

In one non-limiting exemplary embodiment, the cathode feed tube (2145),the recuperator baffle (2215) and each of the bottom end caps (2100) areformed from a high temperature metal alloy that is chromium free andresistance to corrosion; e.g. a Monel alloy. Additionally at least abottom surface of the combustor end wall (2140) which forms a topsurface of the recuperator chamber (2210) is formal by or lined by aprotective element formed from a high temperature metal alloy that ischromium free and resistant to corrosion; e.g. a Monel alloy. Similarlyat least a top surface of the bottom tube support wall (2075) whichforms a bottom surface of the cathode chamber (2090) is formed by orlined by a protective element formed from a high temperature metal alloythat is chromium free and resistance to corrosion; e.g. a Monel.

Internal surfaces associated with incoming air flow that are coated withthe above descried electro-deposited nickel plating layer can be exposedto air flow without exposure to chromium. Nickel plated surfaces thatmay contact incoming air flow include the cylindrical side wall (2002)which forms the sidewall of each of the recuperator chamber (2210) andthe cathode chamber (2090), and the disk shaped bottom wall (2006) whichforms the bottom wall of the recuperator chamber (2210). The surfaceseach have a cross-section (5005) shown in FIG. 5A. Additionally othersurfaces inside the cathode chamber (2090) formed by chromium containingmaterials such as the top tube support wall (2070) and the top end caps(2095) which am each formed from Inconel are covered by a layer ofnickel plating applied to a thickness of 0.0005 to 0.0015 inches. (12.5to 38.1 μm) by electro-deposition plating or the like in order to avoidair contamination with chromium.

Referring now to FIG. 5C a detailed section view depicts a section(5040) taken through the bottom tube support wall (2075). The detailedsection view shows the thermally conductive mass (2180) which comprisesa copper mass having a thermal conductivity approximately ranging from370 W/(m° K) at 500° C. and 332 W/(m° K) at 1027° C. The copper mass(2180) has a thickness in the range of 0.01-0.375 inches (2.5-9.5 mm)however other thicknesses are usable without deviating from the present,invention. A top surface of the wall (2075) fact's the inside of thecathode chamber (2090) and is therefore lined with a disk shaped linerelement (5045) formed from a high temperature metal alloy that ischromium free and resistant to corrosion; e.g. a Monel alloy in order toavoid contaminating the cathode gas with chromium. A bottom surface ofthe wall (2075) faces the tail gas combustion region (2135) and is linedwith a disk shaped liner (5050) formed from a Hastelloy alloy.

Referring now to FIG. 5D a non-limiting exemplary detailed section viewdepicts a section (5055) taken through the combustor end wall (2175).The detailed section shows the thermally conductive mass (2140) whichcomprises a copper mass having a thermal conductivity approximatelyranging from 370 W/(m° K) at 500° C. and 332 W/(m° K) at 1027° C. Thecopper mass (2175) has a thickness in the range of 0.01-0.375 inches(2.5-9.5 mm) however other thicknesses are usable without deviating fromthe present invention. A top surface of the wall (2140) faces the insideof the tail gas combustor region (2135) and is therefore lined with anannular liner element (5060) formed from a solid Hastelloy alloy. Abottom surface of the wall (2140) faces the recuperator chamber (2210)and is lined with an annular liner (5065) formed from a high temperaturemetal alloy that is chromium free and resistant to corrosion; e.g. aMonel alloy.

Referring now to FIG. 5E a non-limiting exemplary detailed section viewdepicts a section (5070) taken through the fuel input manifold top wall(2170). The detail section view shows the thermally conductive mass(2160) which comprises a copper mass having a thermal conductivityapproximately ranging from 370 W/(m° K) at 500° C. and 332 W/(m° K) at1027° C. The copper mass (2160) has a thickness in the range of0.01-0.375 inches (2.5-9.5 mm) however other thicknesses are usablewithout deviating from the present invention. Opposing top and bottomsurfaces of the copper mass (2160) are optionally covered by a layer ofnickel plating (5075) applied to a thickness of 0.0005 to 0.0015 inches,(12.5 to 38.1 μm) by electro-deposition plating or the like. The nickelplating is applied in order to avoid contact between fuel (2025) and thecopper mass (2160) to avoid oxidizing the copper mass surfaces. A topsurface of the wall (2170) faces the inside of the annular cold startcombustion cavity (2305) and is therefore lined with an annular linerelement (5080) formed from a solid Hastelloy alloy to protect thethermal mass (2160) from thermal damage.

A further variation of the walls (2075) and (2175) shown in detail inFIGS. 5C and 5D is that both sides of the copper mass (2180) and (2175)are covered by a layer of nickel plating applied to a thickness of0.0005 to 0.0015 inches. (12.5 to 38.1 μm) by electro-deposition platingor the like as described above e.g. with respect to FIG. 5B. The nickelplating is included in order to avoid contact between fuel (2025) and orair (2200) and the corresponding copper mass (2180) and (2175) so thatoxidizing the copper mass surfaces is avoided. In cases where theHastelloy elements (5050) and (5060) and the Monel elements (5045) and(5065) comprise separate liner elements, i.e. not integrally formed withthe copper mass (2180), the copper mass is preferably nickel plated onboth of its opposing surfaces (e.g. as shown in FIG. 5A). However inother cases where the disk or annular shaped liner elements (5045),(5050), (5060), (5065) are integrally formed with the copper mass (2180)and or (2175) nickel plating the copper mass may not be needed.

Generally Hastelloy and Monel elements described above are used toprotect various surfaces from damage or to avoid contaminating incomingair by contact with chromium containing surfaces such as Inconel orHastelloy surfaces. In one non-limiting example embodiment one or moreprotective elements is fabricated separately from the hot zone enclosurewalls (2015) and installed in place at assembly such as by brazing aprotective material layer onto a surface being protected. In the examplecopper mass (2180, 2175) shown in FIGS. 5C and 5D the protective Moneland Hastelloy layers are brazed directly to opposing surfaces of thecopper mass without nickel plating the copper mass. Preferably thebrazing step substantially gas seals the copper mass preventing air orfuel from contacting and oxidizing surfaces of the copper mass.

In the example copper mass (2160) shown in FIG. 5E the protectiveHastelloy layer is brazed directly to a nickel layer (5070) of onesurface of the copper mass that is disposed inside the combustion region(2135). In this non-limiting example embodiment the Hastelloy layer isinstalled to protect the copper mass surface from direct exposure tocombustion and corrosive elements. On the opposing surface, only anickel plated protective layer (5070) is applied onto the copper masssurface which is disposed inside the recuperator chamber 12210) sinceonly a nickel layer Is needed to protect the copper mass surface fromoxidation by incoming air. In the example of FIG. 5E the Hastelloy layer(5080) can be mechanically attached, e.g. by fasteners or clamped inplace, without the need to gas seal the copper surface since the coppersurface is already protected by the nickel layer (5075) disposed betweenthe coper mass (2160) and the Hastelloy layer (5080).

Thus as described above, and particularly with respect to FIGS. 5B, 5C,5D and 5E the Hastelloy and Monel elements may include a plurality ofseparate elements such as disk shaped elements (5040), (5050) (5060),(5065) (5080) in mating contact with disk shaped thermal mass elements(2180), (2175), (2160) or the Hastelloy and Monel elements may includecylindrical wall portions e.g. (5030) disposed in mating contact withinternal cylindrical wall surfaces of combustion chambers such as thecylindrical sidewall (2002) of the hot zone enclosure walls. Thecylindrical wall portions are inserted in appropriate positions insidethe hot zone enclosure walls, e.g. inside the cold start combustorchamber (2305) and inside the tail gas combustor region (2135) andbrazed, welded or otherwise fastened or clamped in place in matingcontact with surfaces being protected. In some embodiments the Hastelloyand Monel elements may be applied directly to the conductive coresurface (e.g. brazed directly onto a surface of the thermally conductivemass) with a substantially gas tight seal. In other embodiments thethermally conductive mass or core wall surface is nickel plated and theHastelloy or Monel elements may be applied over the nickel platingwithout the need to provide a substantially gas seal and instead ofbrazing over the entire surface to provide a gas seal the elements maybe held in place by clamping, by mechanical fasteners or by brazed orspot welded at selected points. In further embodiments any of the abovedescribed wall structured may be formed as a metal casting with variousprotective material layers formed on selected surfaces of the metalcasting by well-known methods including plating, sputtering, spraycoating hot dipping or the like.

However in other non-limiting embodiments of the present inventionportions of the external and or internal walls of the hot zone enclosurewalls (2015) are formed from prefabricated multi-layered compositematerials. The composite materials including plate and or tubing stockfabricated with a plurality of dissimilar metals layers which are usableto form various hot zone enclosure walls described herein.

In a first step sheets of dissimilar metals are joined together by anextrusion or rolling process generally referred to as cladding. In anexample embodiment, referring to FIG. 5C, a composite sheet comprising acopper mass (2180), a Hastelloy alloy layer (5050) and a Monel alloylayer (5045) are roll welded to form the composite sheet. Once formed,the wall (2075) may be cut from the composite sheet and holes and otherfeatures added in secondary operations. The wall (2075) is thenassembled to the hot zone enclosure walls (2015) by brazing, welding,mechanical fastening, clamping, high temperature adhesive bonding or thelike. Additionally the wall (2175), shown in FIG. 5D, includes the samematerial layers as the wall (2075) shown in FIG. 5C only in reverseorder, may be cut from the same composite sheet and holes and otherfeatures added in secondary operations. Each of the wall (2175) and(2075) is then assembled to the hot zone enclosure walls (2015) bybrazing, welding, mechanical fastening, clamping, high temperatureadhesive bonding or the like.

In an example embodiment, referring to FIG. 5E, a composite sheetcomprising a copper mass (2160) and a Hastelloy alloy layer (5070) areroll welded to form a composite sheet. In this example embodiment thenickel layer (5075) may be omitted such that the composite sheet hasonly two layers. Once formed, the wall (2170) may be cut from thecomposite sheet and holes and other features added in secondaryoperations. The wall (2170) is then assembled to the hot zone enclosurewalls (2015) by brazing, welding, mechanical fastening, clamping, hightemperature adhesive bonding or the like. In a further step thecomposite sheet may be nickel plated on at least the copper surface toprevent oxidation of the exposed copper surface.

Similarly referring to FIG. 5B, a two layer composite sheet comprising acopper core (5010) and a Hastelloy layer (5030) are roll welded to forma composite sheet. In this example embodiment the nickel layer (5015)and (5020) may be omitted such that the composite sheet has only twolayers. Once formed, holes and other features are formed by secondaryoperations and then the composite sheet is formed into a cylindricalwall. The cylindrical wall is cut to size and assembled with othercylindrical wall sections to form portions of the hot zone enclosureside wall (2002) associated with enclosing a combustion region. Thecylindrical wall portions may be joined together by brazing, welding,mechanical fastening, clamping, high temperature adhesive bonding or thelike. In a further step the composite sheet may be nickel plated on oneor both sides and the assembled host zone enclosure side wall may benickel plated to protect, exposed copper surfaces from oxidation.

5.9 FURTHER SOFC FUEL CELL STACK CONFIGURATIONS

Referring now to FIG. 6 portions of a non-limiting exemplary embodimentof a SOFC system embodiment (7000) usable with the present invention areshown in a top section view. The configuration (7000) depicts a cathodechamber (7010) enclosed by a circular hot zone enclosure wall (7015)shown in lop section view. The circular enclosure wall (7015) issurrounded by a circular thermal insulation layer (7020) separated fromthe circular enclosure wall by a small air gap, not shown, usable as agas (low conduit as described above.

A cathode feed tube (7025) is shown centered with respect to thecircular hot zone enclosure wall (7015). A plurality of rod shaped fuelcells is disposed in two concentric circular patterns with each circularpattern centered with respect to the same center axes (7030). An innercircular pattern (7035) includes eight inner rod shaped fuel cells(7040). An outer circular pattern (7045) includes fourteen outer rodshaped fuel cells (7050). Other enclosure shapes and fuel cell patternsare usable without deviating from the present invention.

It will also be recognized by those skilled in the art that, while theinvention has been described above in terms of preferred embodiments, itis not limited thereto. Various features and aspects of the abovedescribed invention may be used individually or jointly. Further,although the invention has been described in the context of itsimplementation in a particular environment, and for particularapplications (e.g. Solid oxide fuel cell systems), those skilled in theart will recognize that its usefulness is not limited thereto and thatthe present invention can be beneficially utilized in any number ofenvironments and implementations where it is desirable to increasethermal energy transfer by thermal conduction using high thermalconductivity materials at

1-30. (canceled)
 31. A Solid Oxide Fuel Cell (SOFC) system comprising: hot zone enclosure walls enclosing a hot zone cavity; a top tube support wall attached to a surface of the hot zone enclosure walls; a bottom tube support wall attached to a surface of the hot zone enclosure walls; a SOFC stack comprising a plurality of fuel cells supported between the top tube support wall and the bottom tube support wall; a cathode chamber formed between the top tube support wall and the bottom tube support wall; wherein the bottom tube support wall comprises a first thermal mass formed from one or more thermally conductive materials having a coefficient of thermal conductivity of 100 W/mK.
 32. The SOFC system of claim 31 wherein the hot zone cavity includes a combustion region bounded by a portion of the hot zone enclosure walls, the bottom tube support wall, and a combustor end wall disposed opposed to the bottom support wall.
 33. The SOFC system of claim 32 wherein the hot zone enclosure cavity includes a recuperator chamber bounded by a portion of the hot zone enclosure walls, the combustor end wall and a hot zone enclosure bottom wall disposed opposed to the combustor end wall.
 34. The SOFC system of claim 32 wherein: the combustion region confines combustion of a mixture of spent fuel and oxygen depleted cathode air therein; the combustion of the mixture generates thermal energy that is transferred, from the combustion inside the combustion region, to the first thermal mass, by thermal convection or by thermal radiation; the thermal energy, received by the first thermal mass, from the combustion inside the combustion region, is transferred, from the first thermal mass, to cathode air contained within the cathode chamber by thermal convection or by thermal radiation.
 35. The SOFC system of claim 33 wherein: the combustion region confines combustion of a mixture of spent fuel and oxygen depleted cathode air therein; the combustion of the mixture generates thermal energy that is transferred, from the combustion inside the combustion region, to the second thermal mass, by thermal convection or by thermal radiation; the thermal energy, received by the second thermal mass, from the combustion inside the combustion region, is transferred from the second thermal mass to cathode air contained within the recuperator chamber by thermal convection or by thermal radiation.
 36. The SOFC system of claim 31 wherein, the hot zone enclosure walls are formed to provide one or more thermally conductive pathways extending between different regions of the hot zone enclosure walls; are formed from one or more thermally conductive materials having a coefficient of thermal conductivity of 100 W/mK or greater; wherein the first thermal mass is thermally conductively coupled to at least one of the hot zone enclosure walls; wherein thermal energy received by the first thermal mass is transferred, from the first thermal mass, to the hot zone enclosure walls by thermal conduction, and transferred, from the hot zone enclosure walls, to cathode air contained within the cathode chamber, by thermal convection or by thermal radiation.
 37. The SOFC system of claim 33 wherein the hot zone enclosure walls are formed to provide one or more thermally conductive pathways extending between different regions of the hot zone enclosure walls; are formed from one or more thermally conductive materials having a coefficient of thermal conductivity of 100 W/mK or greater; wherein the second thermal mass is thermally conductively coupled to at least one of the hot zone enclosure walls; wherein thermal energy received by the second thermal mass is transferred from, the second thermal mass, to the hot zone enclosure walls by thermal conduction, and transferred, from the hot zone enclosure walls to cathode air contained within the recuperator chamber, by thermal convection or by thermal radiation.
 38. The SOFC system of claim 31 further comprising a first top protective surface layer (5040) covering a top surface of the first thermal mass, wherein the first top protective surface layer is thermally conductively coupled to the top surface of the first thermal mass.
 39. The SOFC system of claim 38 wherein the first top protective surface layer comprises a chromium free metal.
 40. The SOFC system of claim 31 further comprising a first bottom protective surface layer covering a bottom surface of the first thermal mass, wherein the first bottom protective surface layer is thermally conductively coupled to the bottom surface of the first thermal mass.
 41. The SOFC system of claim 40 wherein the first bottom protective surface layer (5050) comprises a metal.
 42. The SOFC system of claim 31 further comprising a second top protective surface layer covering a top surface of the second thermal mass, wherein the second top protective surface layer is thermally conductively coupled to the top surface of the second thermal mass.
 43. The SOFC system of claim 32 wherein the second top protective surface layer comprises a metal.
 44. The SOFC system of claim 31 further comprising a second bottom protective surface layer covering a bottom surface of the second thermal mass, wherein the second bottom protective surface layer is thermally conductively coupled to the bottom surface of the second thermal mass.
 45. The SOFC system of claim 44 wherein the second bottom protective surface layer comprises a chromium free metal.
 46. A method for thermal energy distribution for a Solid Oxide Fuel Cell (SOFC) system comprising the steps of: forming a plurality of hot zone enclosure walls to enclose a hot zone cavity; attaching a top tube support wall to a surface of the hot zone enclosure walls inside the hot zone cavity; attaching a bottom tube support wall to a surface of the hot zone enclosure walls inside the hot zone cavity; supporting, a SOFC stack comprising a plurality of fuel cells, inside the hot zone cavity, between the top tube support wall and the bottom tube support wall; forming, between the top tube support wall and the bottom tub support wall, inside the hot zone cavity, a cathode chamber, for receiving cathode air therein; forming, the bottom tube support wall to include a first thermal mass formed from one or more thermally conductive materials having a coefficient of thermal conductivity of 100 W/m K.
 47. The method of claim 46 further comprising forming, inside the hot zone cavity, a combustion region bounded by each of, a portion of the hot zone enclosure walls, the bottom tube support wall, and a combustor end wall disposed opposed to the bottom support wall.
 48. The method of claim 47 further comprising forming, inside the hot zone cavity, a recuperator chamber bounded by, each of, a portion of the hot zone enclosure walls, the combustor end wall and a hot zone enclosure bottom wall disposed opposed to the combustor end wall.
 49. The SOFC system of claim 47 further comprising the steps of: combusting, inside the combustion region, a mixture of spent fuel, received into the combustion region from the SOFC stack, and oxygen depleted cathode air, received into the cathode chamber from the cathode chamber; transferring thermal energy generated inside the combustion region to the first thermal mass by thermal convection or by thermal radiation; transferring the thermal energy, received by the first thermal mass from inside the combustion region, to cathode air contained inside the cathode chamber by thermal convection or by thermal radiation.
 50. The method of claim 48 further comprising the steps of: combusting, inside the combustion region, a mixture of, spent fuel, received into the combustion region from the SOFC stack, and oxygen depleted cathode air, received into the combustion region from the cathode chamber; transferring thermal energy generated inside the combustion region to the second thermal mass by thermal convection or by thermal radiation; transferring the thermal energy, received by the second thermal mass from inside the combustion region, to cathode air contained within the recuperator chamber by thermal convection or by thermal radiation.
 51. The method of claim 46 further comprising the steps of: forming the hot zone enclosure walls to provide one or more thermally conductive pathways extending between different regions of the hot zone enclosure walls; forming the one or more thermally conductive pathways to include one or more thermally conductive materials having a coefficient of thermal conductivity of 100 W/mK or greater; thermally conductively coupling the first thermal mass to an inside surface of at least one of the hot zone enclosure walls; transferring thermal energy, between the first thermal mass and the hot zone enclosure walls by thermal conduction; transferred thermal energy, from the hot zone enclosure walls, to cathode air inside the cathode chamber and to surfaces of the SOFC stack by thermal convection or by thermal radiation.
 52. The method of claim 48 further comprising the steps of: forming the hot zone enclosure walls to provide one or more thermally conductive pathways extending between different regions of the hot zone enclosure walls; forming the one or more thermally conductive pathways to include one or more thermally conductive materials having a coefficient of thermal conductivity of 100 W/mK or greater; thermally conductively coupling the second thermal mass an inside surface of at least one of the hot zone enclosure walls; transferring thermal energy, between the second thermal mass and the hot zone enclosure walls by thermal conduction; transferring thermal energy, from the hot zone enclosure walls, to cathode air inside the recuperator chamber by thermal convection or by thermal radiation.
 53. The method of claim 16 further comprising the steps of: covering a top surface of the first thermal mass with a first top protective surface layer (5040), wherein the first top protective surface layer is thermally conductively coupled to the top surface of the first thermal mass.
 54. The method of claim 23 wherein the first top protective surface layer comprises a chromium free metal.
 55. The method of claim 46 further comprising the steps of: covering a bottom surface of the first thermal mass with a first bottom protective surface layer, wherein the first bottom protective surface layer is thermally conductively coupled to the bottom surface of the first thermal mass.
 56. The method of claim 55 wherein the first bottom protective surface layer comprises a metal.
 57. The method of claim 46 further comprising the step of covering a top surface of the second thermal mass with a second top protective surface layer, wherein the second top protective surface layer is thermally conductively coupled to the top surface of the second thermal mass.
 58. The method of claim 57 wherein the second top protective surface layer comprises a metal.
 59. The method of claim 16 further comprising the step of covering a bottom surface of the second thermal mass with a second bottom protective surface layer, wherein the second bottom protective surface layer is thermally conductively coupled to the bottom surface of the second thermal mass.
 60. The method of claim 59 wherein the second bottom protective surface layer comprises a chromium free metal.
 61. A Solid Oxide Fuel Cell (SOFC) system comprising: hot zone enclosure walls enclosing a hot zone cavity, wherein the hot zone enclosure walls are formed to include one or more thermally conductive pathways extending between different regions of the hot zone enclosure walls and wherein the one or more thermally conductive pathways are formed to include one or more thermally conductive materials having a coefficient of thermal conductivity of 100 W/mK or greater; a bottom tube support wall attached to a surface of the hot zone enclosure walls; a SOFC stack comprising a plurality of fuel cells supported to extend from the bottom tube support wall; wherein the bottom tube support wall comprises a first thermal mass formed from one or more thermally conductive materials having a coefficient of thermal conductivity of 100 W/mK and wherein the first thermal mass is thermally conductively coupled to at least one of the one or more thermally conductive pathways; wherein thermal energy is transferred by thermal conduction, between the first thermal mass, and at least one of the one or more thermally conductive pathways extending between different regions of the hot zone enclosure walls. 